//
// virtio device definitions.
// for both the mmio interface, and virtio descriptors.
// only tested with qemu.
//
// the virtio spec:
// https://docs.oasis-open.org/virtio/virtio/v1.1/virtio-v1.1.pdf
//

// virtio mmio control registers, mapped starting at 0x10001000.
// from qemu virtio_mmio.h
#define VIRTIO_MMIO_MAGIC_VALUE 0x000 // 0x74726976
#define VIRTIO_MMIO_VERSION 0x004     // version; should be 2
#define VIRTIO_MMIO_DEVICE_ID 0x008   // device type; 1 is net, 2 is disk
#define VIRTIO_MMIO_VENDOR_ID 0x00c   // 0x554d4551
#define VIRTIO_MMIO_DEVICE_FEATURES 0x010
#define VIRTIO_MMIO_DRIVER_FEATURES 0x020
#define VIRTIO_MMIO_QUEUE_SEL 0x030        // select queue, write-only
#define VIRTIO_MMIO_QUEUE_NUM_MAX 0x034    // max size of current queue, read-only
#define VIRTIO_MMIO_QUEUE_NUM 0x038        // size of current queue, write-only
#define VIRTIO_MMIO_QUEUE_READY 0x044      // ready bit
#define VIRTIO_MMIO_QUEUE_NOTIFY 0x050     // write-only
#define VIRTIO_MMIO_INTERRUPT_STATUS 0x060 // read-only
#define VIRTIO_MMIO_INTERRUPT_ACK 0x064    // write-only
#define VIRTIO_MMIO_STATUS 0x070           // read/write
#define VIRTIO_MMIO_QUEUE_DESC_LOW 0x080   // physical address for descriptor table, write-only
#define VIRTIO_MMIO_QUEUE_DESC_HIGH 0x084
#define VIRTIO_MMIO_DRIVER_DESC_LOW 0x090 // physical address for available ring, write-only
#define VIRTIO_MMIO_DRIVER_DESC_HIGH 0x094
#define VIRTIO_MMIO_DEVICE_DESC_LOW 0x0a0 // physical address for used ring, write-only
#define VIRTIO_MMIO_DEVICE_DESC_HIGH 0x0a4

// status register bits, from qemu virtio_config.h
#define VIRTIO_CONFIG_S_ACKNOWLEDGE 1
#define VIRTIO_CONFIG_S_DRIVER 2
#define VIRTIO_CONFIG_S_DRIVER_OK 4
#define VIRTIO_CONFIG_S_FEATURES_OK 8

// device feature bits
#define VIRTIO_BLK_F_RO 5          /* Disk is read-only */
#define VIRTIO_BLK_F_SCSI 7        /* Supports scsi command passthru */
#define VIRTIO_BLK_F_CONFIG_WCE 11 /* Writeback mode available in config */
#define VIRTIO_BLK_F_MQ 12         /* support more than one vq */
#define VIRTIO_F_ANY_LAYOUT 27
#define VIRTIO_RING_F_INDIRECT_DESC 28
#define VIRTIO_RING_F_EVENT_IDX 29

// this many virtio descriptors.
// must be a power of two.
#define NUM 8

// a single descriptor, from the spec.
struct virtq_desc
{
    uint64 addr;
    uint32 len;
    uint16 flags;
    uint16 next;
};
#define VRING_DESC_F_NEXT 1  // chained with another descriptor
#define VRING_DESC_F_WRITE 2 // device writes (vs read)

// the (entire) avail ring, from the spec.
struct virtq_avail
{
    uint16 flags;     // always zero
    uint16 idx;       // driver will write ring[idx] next
    uint16 ring[NUM]; // descriptor numbers of chain heads
    uint16 unused;
};

// one entry in the "used" ring, with which the
// device tells the driver about completed requests.
struct virtq_used_elem
{
    uint32 id; // index of start of completed descriptor chain
    uint32 len;
};

struct virtq_used
{
    uint16 flags; // always zero
    uint16 idx;   // device increments when it adds a ring[] entry
    struct virtq_used_elem ring[NUM];
};

// these are specific to virtio block devices, e.g. disks,
// described in Section 5.2 of the spec.

#define VIRTIO_BLK_T_IN 0  // read the disk
#define VIRTIO_BLK_T_OUT 1 // write the disk

// the format of the first descriptor in a disk request.
// to be followed by two more descriptors containing
// the block, and a one-byte status.
struct virtio_blk_req
{
    uint32 type; // VIRTIO_BLK_T_IN or ..._OUT
    uint32 reserved;
    uint64 sector;
};
